Polyurethane systems for producing polyurethane sandwich parts at low molding temperatures

ABSTRACT

The present invention relates to the use of a polyurethane system, comprising (a) polyisocyanates, (b) at least one isocyanate-reactive compound, (c) at least one carboxylic salt of an amine catalyst, where, based on one equivalent of the amine of the amino catalyst, from 0.5 to 1.5 equivalents of acid groups of a carboxylic acid are comprised, (d) if appropriate, further catalysts, (e) if appropriate, a reactive chain extender having at least two groups reactive toward isocyanates, where at least one group reactive toward isocyanates is a free, primary, NH 2  group, and (f) if appropriate, further additives, for the production of polyurethane sandwich components. The present invention further relates to a process for the production of polyurethane sandwich components, and also to the polyurethane sandwich components obtained by the process of the invention.

The present invention relates to the use of a polyurethane system,comprising (a) polyisocyanates, (b) at least one isocyanate-reactivecompound, (c) at least one carboxylic salt of an amine catalyst, where,based on one equivalent of the amine of the amino catalyst, from 0.5 to1.5 equivalents of acid groups of a carboxylic acid are comprised, (d)if appropriate, further catalysts, (e) if appropriate, a reactive chainextender having at least two groups reactive toward isocyanates, whereat least one group reactive toward isocyanates is a free, primary, NH₂group, and (f) if appropriate, further additives, for the production ofpolyurethane sandwich components. The present invention further relatesto a process for the production of polyurethane sandwich components, andalso to the polyurethane sandwich components obtained by the process ofthe invention.

Further embodiments of the present invention are found in the claims, inthe description, and in the examples. The abovementioned features of thesubject matter of the invention, and the features that will be explainedbelow, can, of course, be used not only in the respective combinationstated but also in other combinations, without exceeding the scope ofthe invention.

Polyurethane sandwich components have been known for a long time. Theseare produced by covering a core layer with a reinforced layer. Apolyurethane reaction mixture is applied to one side of this“semifinished sandwich product”, and often on both sides, preferably viaspray-application. The component covered with the polyurethane reactionmixture, the unfinished sandwich component, is then placed into a mold,in which the semifinished sandwich product is given a particular shapeby compression in a thermal compression process and the polyurethanereaction mixture is hardened to give the polyurethane. The reinforcementlayer is compacted during this compression process. The extent of thiscompaction can be varied widely, from a few tenths of a millimeter to afew percent of initial thickness in some subregions. The resultantpolyurethane sandwich component is then removed from the mold. Theexternal profile here is shaped by squeezing of the sandwich packagewithin the shaping mold.

So that three-dimensional shaping can be achieved, hardening of thepolyurethane reaction mixture must be delayed until the material hasreached the mold. In particular in the region of the edges of thesecompressed regions, the core layer can be sealed by polyurethane only ifsufficient flowable polyurethane reaction mixture is present, after thecompression process, to cover said regions. These processes aredescribed by way of example in the brochure “PUR—Faserverbundwerkstoffefür den Leichtbau im Fahrzeuginnenraum” [“PU—Fiber composite materialsfor lightweight construction in vehicle interiors”] from Bayer AGLeverkusen (order number: PU 52248) or “Baypreg F—PUR plus Natur imAutomobil, Verbundwerkstoffe aus Polyurethan” [“Baypreg F—PU plusnatural materials in automobiles: polyurethane composite materials”]from Bayer AG Leverkusen.

A problem with the known process is that the shaping process has to becarried out at mold temperatures of from about 120 to 140° C., in orderto ensure the necessary short demolding times for industrial purposes,without shortening the polyurethane system processing time needed forthe production of the unfinished sandwich component, the “open time”,and without impairing the necessary flowability of the polyurethanereaction mixture in the mold. However, these high mold temperatures leadto energy consumption in the production of the polyurethane sandwichcomponent; another factor is that direct lamination is possible onlyusing very expensive, heat-resistant decorative materials.

It was an object of the present invention to reduce energy consumptionand improve direct lamination behavior in the production of polyurethanesandwich components, without shortening the open time or lengthening thedemolding times, in comparison with known processes.

The object of the invention is achieved via the use of a polyurethanesystem, comprising (a) polyisocyanates, (b) at least oneisocyanate-reactive compound, (c) at least one carboxylic salt of anamine catalyst, (d) if appropriate, further catalysts, (e) ifappropriate, a reactive chain extender having at least two groupsreactive toward isocyanates, where at least one group reactive towardisocyanates is a free, primary NH₂ group, and (f) if appropriate,further additives, for the production of polyurethane sandwichcomponents, where, based on one equivalent of amine of the aminecatalyst, from 0.5 to 1.5 equivalents of acid groups of a carboxylicacid are comprised.

For the purposes of the invention, a polyurethane system is a systemcomposed of at least two components, where the polyurethane reactionmixture of the invention is obtained on mixing of the components.Components (b) to (f) here are often combined to give what is known as apolyol component, component (a) being termed isocyanate component.

Polyisocyanates used preferably comprise aromatic isocyanates. It ispreferable to use aromatic isocyanates of the general formulaR(NCO)_(z), where R is a polyvalent organic radical which comprises anaromatic system, and z is a whole number which is at least 2. Exampleshere are 4,4′-diisocyanatobenzene, 1,3-diisocyanato-o-xylene,1,3-diisocyanato-p-xylene, 1,3-diisocyanato-m-xylene,2,4-diisocyanato-1-chlorobenzene, 2,4-diisocyanato-1-nitrobenzene,2,5-diisocyanato-1-nitrobenzene, m-phenylene diisocyanate, p-phenylenediisocyanate, toluene 2,4-diisocyanate, toluene 2,6-diisocyanate,mixtures composed of toluene 2,4- and 2,6-diisocyanate, naphthalene1,5-diisocyanate, 1-methoxyphenylene 2,4-diisocyanate, diphenylmethane4,4′-diisocyanate, diphenylmethane 2,4′-diisocyanate, biphenylene4,4′-diisocyanate, 3,3′-dimethyldiphenylmethane 4,4′-diisocyanate;triisocyanates, such triphenylmethane 4,4′,4″-triisocyanate and toluene2,4,6-triisocyanate, and tetraisocyanates, such as4,4′-dimethyldiphenylmethane 2,2′,5,5′-tetraisocyanate. Particularpreference is given to toluene diisocyanates, diphenylmethane2,4′-diisocyanate, diphenylmethane 4,4′-diisocyanate, polymethylenepolyphenylene polyisocyanate, and also to derivatives and mixturesthereof.

It is preferable to use isocyanates having a relatively high number ofaromatic nuclei, particular preference being given to polymethylenepolyphenylene polyisocyanate, also termed polymer MDI. These can also beprepolymerized prior to use, using polyetherols or polyesterols, to giveisocyanate prepolymers, in order to establish specific properties. It isalso possible to use crude MDI.

A modified, polyvalent isocyanate in particular used comprises reactionproducts of polymer MDI and of polyesterols, as described under (b). Thefunctionalities of the isocyanate component here are from 1.2 to 3.0,preferably from 1.5 to 3.0, particularly preferably from 2.0 to 2.8.

The isocyanate-reactive compound (b) used can comprise any compound thatcan be used in polyurethane production and that has at least twohydrogen atoms reactive toward isocyanates. The isocyanate-reactivecompound (b) used preferably comprises a polyether polyol, a polyesterpolyol, an amine-functionalized compound, or a mixture thereof.Polyether polyols are particularly preferred.

Suitable polyether polyols can be prepared by known processes, forexample via anionic polymerization using alkali metal hydroxides, suchas sodium hydroxide or potassium hydroxide, or using alkali metalalcoholates, such as sodium methoxide, sodium ethoxide or potassiumethoxide, or potassium propoxide as catalysts, with addition of at leastone starter molecule which comprises from 2 to 8 reactive hydrogenatoms, or via cationic polymerization using Lewis acids, such asantimony pentachloride, boron fluoride etherate, etc., or bleachingearth as catalysts, from one or more alkylene oxides having from 2 to 4carbon atoms in the alkylene radical. The catalysts used can alsocomprise multimetal cyanide compounds, known as DMC catalysts.

Examples of suitable alkylene oxides are tetrahydrofuran, propylene1,3-oxide, butylene 1,2-oxide or butylene 2,3-oxide, styrene oxide, andpreferably ethylene oxide and propylene 1,2-oxide. The alkylene oxidescan be used individually, in alternating succession, or as a mixture.

Examples of starter molecules that can be used are: water, organicdicarboxylic acids, such as succinic acid, adipic acid, phthalic acid,and terephthalic acid, aliphatic and aromatic, optionally N-mono-, N,N-,and N,N′-dialkyl-substituted diamines having from 1 to 4 carbon atoms inthe alkyl radical, e.g. optionally mono- and dialkyl-substitutedethylenediamine, diethylenetriamine, triethylenetetramine,1,3-propylenediamine, 1,3- or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-,1,5-, and 1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4-, and2,6-tolylenediamine, and 4,4′-, 2,4′-, and 2,2′-diaminodiphenylmethane.

Other starter molecules that can be used are: alkanolamines, such asethanolamine, diethanolamine, N-methyl- and N-ethylethanolamine,N-methyl- and N-ethyldiethanol-amine, and triethanolamine, and ammonia.Preference is given to use of polyhydric, in particular di- tooctahydric, alcohols, e.g. ethanediol, 1,2- and 1,3-propanediol,diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol,glycerol, trimethylolpropane, pentaerytritol, glucose, fructose andsucrose.

The polyether polyols, preferably polyoxyethylene polyols,polyoxypropylene polyols and polyoxypropylene polyoxyethylene polyols,have an average functionality of from 1.5 to 5.0, preferably from 1.8 to4.2, and in particular from 2.0 to 3.5, and have number-averagemolecular weights which are preferably from 32 to 1500, particularlypreferably from 60 to 1000, and in particular from 60 to 800. Thedifferent functionalities here are preferably obtained via the use ofdifferent starters.

Other suitable polyols are polymer-modified polyols, preferablypolymer-modified polyesterols or polyetherols, particularly preferablygraft polyetherols. These are what is known as a polymer polyol, whichusually has from 5 to 50% by weight, preferably from 10 to 45% byweight, particularly preferably from 15 to 25% by weight and inparticular from 18 to 22% by weight, content of polymers which arepreferably thermoplastic. These polymer polyesterols are described byway of example in EP-A-250 351 and are usually prepared via free-radicalpolymerization of suitable olefinic monomers, such as styrene,acrylonitrile, acrylates, and/or acrylamide, are generally via transferof the free radicals of growing polymer chains onto polyesterols orpolyetherols. The polymer polyol mainly comprises, alongside the graftcopolymer, the homopolymers of the olefins, dispersed in unalteredpolyesterol.

One preferred embodiment uses acrylonitrile and styrene as monomers, andin particular uses exclusively styrene. The monomers are polymerized, ifappropriate, in the presence of further monomers, of a macromer, and ofa moderator, and using a free-radical initiator, mostly azo compounds orperoxide compounds, in a polyesterol as continuous phase.

During the free-radical polymerization reaction, the macromers areconcomitantly incorporated into the copolymer chain. The result isformation of block copolymers having a polyester block and apolyacrylonitrile-styrene block, these acting as compatibilizer in theboundary between continuous phase and disperse phase and suppressingagglomeration of the polymer polyesterol particles. The proportion ofthe macromers is usually from 1 to 15% by weight, based on the totalweight of the monomers used for preparation of the polymer polyol.

The proportion of polymer polyol is preferably greater than 5% byweight, based on the total weight of component (b). The material can, byway of example, comprise an amount of from 30 to 90% by weight,preferably from 55 to 80% by weight, of the polymer polyols, based onthe total weight of component (b). It is particularly preferable thatthe polymer polyol is polymer polyesterol or is polyetherol.

The carboxylic salt used of an amine catalyst (c) can comprisecarboxylic salts of any of the conventional basic amine catalysts usedfor polyurethane production. The carboxylic salts of the basic aminecatalysts are obtained here by mixing the amine catalysts withcarboxylic acids. This can take place in a separate step, if appropriateusing a solvent, or via addition of the acid and of the basic aminecatalyst to the polyol component.

The carboxylic salt of the amine catalyst is preferably obtained bymixing carboxylic acid and basic amine catalyst in a separate step, ifappropriate with heating. It is preferable here to use an alcohol assolvent, particularly preferably a di- or trihydric alcohol whose molarmass is smaller than 120 g/mol, in particular ethylene glycol. Theresultant carboxylic salt of an amine catalyst can then, in a furtherstep, be combined with at least the component (b), and also, ifappropriate, with one of components (d), (e), and (f), to give thepolyol component.

Basic amine catalysts are described by way of example in“Kunststoffhandbuch [Plastics handbook], volume 7, Polyurethane[Polyurethanes], Carl Hanser Verlag, 3^(rd) edition 1993, chapter 3.4.1.Examples of these are amidines, such as2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines, such astriethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-,N-cyclohexylmorpholine, N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethylbutanediamine, N,N,N′,N′-tetramethylhexanediamine,pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether,bis(dimethylaminopropyl)urea,N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine, dimethylpiperazine,1,2-dimethylimidazole, 1-azabicyclo[3.3.0]-octane and preferably1,4-diazabicyclo[2.2.2]octane and alkanolamine compounds, such astriethanolamine, triisopropanolamine, N-methyl- andN-ethyldiethanolamine N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine,and dimethylethanolamine. Basic amine catalysts which have at least one,preferably precisely one, group reactive toward isocyanates are inparticular used here, an example beingN,N-bis(3-dimethylaminopropyl)-N-isopropanolamine. The catalysts can beused individually or in the form of mixtures.

Carboxylic acids used are preferably those whose molar mass is smallerthan 300 g/mol. It is particularly preferable here to use saturated andunsaturated aliphatic monocarboxylic acids having from 1 to 18 carbonatoms, e.g. formic acid, acetic acid, cyanoacetic acid, or2-ethylhexanoic acid, aromatic carboxylic acids, aliphatic, saturatedand unsaturated dicarboxylic acids having from 2 to 16 carbon atoms, ortricarboxylic acids, or a mixture thereof. Derivatives of theabovementioned carboxylic acids can also be used. Other preferredcarboxylic acids used are dicarboxylic acids of the general formulaHOOC—(CH₂)_(n)—COOH, where n is a whole number from 2 to 14.Dicarboxylic acids of this type are generally less corrosive. Inparticular, the carboxylic acid used comprises adipic acid.

The ratio of acid and amine catalyst here is selected in such a way thatthe number of equivalents of acid groups of a carboxylic acid comprisedis from 0.5 to 1.5, preferably from 0.7 to 1.3, particularly preferablyfrom 0.90 to 1.10, and in particular from 0.95 to 1.05 equivalents,based on one equivalent of amine of the amine catalyst.

An example of a concentration that can be used of the carboxylic saltsof an amine catalyst (c) is from 0.001 to 10% by weight, preferably from0.05 to 5% by weight, and particularly preferably from 0.05 to 2% byweight, based on the weight of components (b) to (f).

Further catalysts (d) that can be used are organic metal compounds,preferably organic tin compounds, such as stannous salts of organiccarboxylic acids, e.g. stannous acetate, stannous octoate, stannousethylhexoate, and stannous laurate, and the dialkyltin(IV) salts ororganic carboxylic acids, e.g. dibutyltin diacetate, dibutyltindilaurate, dibutyltin maleate, and dioctyltin diacetate, and alsobismuth carboxylates, such as bismuth(III) neodecanoate, bismuth2-ethylhexanoate and bismuth octanoate, or a mixture. It is preferableto use no further catalysts (d).

Substances that can be used as reactive chain extenders (e) have twogroups reactive toward isocyanates, and these substances have at leastone free primary NH₂ group. These substances accelerate the polyurethanereaction. The further group reactive toward isocyanate can for examplehave been selected from a primary amino group, an alcohol group, or athiol group. The reactive chain extenders (e) used can by way of examplecomprise aliphatic or aromatic amines. The reactive chain extenders (e)here can be used individually or in the form of mixtures.

In one particularly preferred embodiment, the reactive chain extenders(e) preferably comprise aromatic diamines, in particulartolylenediamines, or derivatives thereof, e.g.3,5-diethyltolylene-2,4-diamine.

In another preferred embodiment, the reactive chain extender (e) isaliphatic and has, between the two groups reactive toward isocyanates,at least two alkylene groups, each having one or two carbon atoms, wherethe alkylene groups are respectively separated by a heteroatom. The twogroups reactive toward isocyanates are in particular amino groups. Themolar mass of the reactive chain extender (e) in this preferredembodiment is preferably from 100 to 400 g/mol, particularly preferablyfrom 100 to 200 g/mol, and in particular from 100 to 150 g/mol. Ifaliphatic reactive chain extenders are used, triethylene glycol diamineis in particular used as reactive chain extender (e).

The proportion of the reactive chain extenders in the polyol componentis preferably from 0.1 to 10% by weight, particularly preferably from0.3 to 8%, more preferably from 0.5 to 5% by weight, and in particularfrom 1.5 to 4.0% by weight, based on the total weight of components (b)to (f).

Alongside the reactive chain extenders (e) it is also possible, ifappropriate, to use reactive crosslinking agents which have at least onefree primary NH₂ group, and which accelerate the polyurethane reaction,and whose functionality is greater than 2.

Alongside the reactive chain extenders (e) of the invention, it ispossible to use further conventional chain extenders. Examples of theseare diols, particularly preferably monoethylene glycol and butanediol.For the purposes of the invention, it is particularly preferable to usemixtures composed of a reactive chain extender of the invention and of achain extender composed of a diol.

Further additives (f) that can be used are blowing agents, additiveshaving thixotropic effect, fillers, antioxidants, dyes, pigments,optical brighteners, and stabilizers with respect to heat, light, and/orUV radiation, and plasticizers or surfactants.

Examples that may be mentioned of suitable release agents are: reactionproducts of fatty acid esters with polyisocyanates, salts composed ofpolysiloxanes comprising amino groups and of fatty acids, salts composedof saturated or unsaturated (cyclo)aliphatic carboxylic acids having atleast 8 carbon atoms and of tertiary amines, and also in particularinternal lubricants, such as carboxylic esters and/or carboxamides,prepared via esterification or amidation of a mixture composed ofmontanic acid and of at least one aliphatic carboxylic acid having atleast 10 carbon atoms, using at least difunctional alkanolamines,polyols and/or polyamines whose molar masses are from 60 to 400 g/mol,as disclosed by way of example in EP 153 639, or using mixtures composedof organic amines, metal salts of stearic acid, and organic mono- and/ordicarboxylic acids or their anhydrides, as disclosed by way of examplein DE-A-3 607 447, or using mixtures composed of an imino compound, ofthe metal salt of a carboxylic acid, and, if appropriate, of acarboxylic acid, as described by way of example in U.S. Pat. No.4,764,537.

Blowing agents used can be any of the blowing agents known for theproduction of polyurethanes. These can comprise chemical and/or physicalblowing agents. These blowing agents are described by way of example in“Kunststoffhandbuch [Plastics handbook], volume 7, Polyurethane[Polyurethanes], Carl Hanser Verlag, 3^(rd) edition 1993, chapter 3.4.5.Chemical blowing agents are compounds which form gaseous products viareaction with isocyanate. Examples of these blowing agents are water orcarboxylic acids. Physical blowing agents here are compounds which arein dissolved or emulsified form in the starting materials forpolyurethane production and vaporize under the conditions ofpolyurethane formation. These are by way of example hydrocarbons,halogenated hydrocarbons, and other compounds such as perfluorinatedalkanes, e.g. perfluorohexane, fluorochlorocarbons, and ethers, esters,ketones, and/or acetals.

The polyurethane systems of the invention are preferably water-blown.The proportion of water in water-blown polyurethane systems is from 0.1to 2.0% by weight, particularly preferably from 0.2 to 1.5% by weight,in particular from 0.4 to 1.1% by weight, based on the total weight ofcomponents (b) to (f).

Examples of antioxidants, and stabilizers with respect to heat, lightand/or UV radiation are stabilizers from the group of the stericallyhindered phenols, e.g. Cyanox 1790® from Cytec Industries INC, HALSstabilizers (hindered amine light stabilizer), triazines, benzophenones,and benzotriazoles. Examples of pigments and matting agents are titaniumdioxide, magnesium stearate, silicone oil, zinc oxide, and bariumsulfate. Examples of dyes are acidic dyes and dispersion dyes.

The present invention further provides a process for the production ofpolyurethane sandwich components by taking (i) a core layer and at leastone reinforcement fiber layer, (ii) applying a polyurethane reactionmixture to the reinforcement fiber layer, (iii) placing the componentfrom (ii) into a mold and hardening the polyurethane reaction mixture inthe mold, (iv) removing the molding from the mold and, if appropriate,subjecting it to further operations, where the polyurethane reactionmixture is obtainable via mixing of the components of a polyurethanesystem of the invention.

A preferred material used here for the core layer is thermoformablepolyurethane foams, or else paper honeycombs, metal honeycombs, orplastics honeycombs. A preferred reinforcement fiber layer used canpreferably comprise glass fiber mats, glass fiber nonwovens, randomglass fiber layers, woven glass fibers, cut or ground glass fibers orcut or ground mineral fibers, natural fiber mats and knitted naturalfibers, cut natural fibers and cut fiber mats, and the correspondingnonwovens and knits based on polymer fibers, or on carbon fibers or onaramid fibers, and also mixtures of these. The reinforcement fiber layerhere can be applied to one side of the core layer or else to both sidesof the core layer.

Polyurethane reaction mixtures, obtainable via mixing of components (a)to (f) of a polyurethane system of the invention, are applied to theresultant semifinished sandwich product. This is preferably achieved viaspray-application of the polyurethane reaction mixture. The viscosity ofthe polyurethane reaction mixture of the invention at 25° C. ispreferably from 280 to 3000 mPas, particularly preferably from 350 to2000 mPas, directly after mixing, and the viscosity rises rapidly about5-10 seconds after the mixing process.

To produce the polyurethane reaction mixture, the individual componentsof the polyurethane system of the invention are mixed in such a way thatthe isocyanate index is from 80 to 200, in particular from 90 to 150.For the purposes of the present invention, the isocyanate index is thestoichiometric ratio of isocyanate groups to isocyanate-reactive groups,multiplied by 100. Isocyanate-reactive groups here are any of theisocyanate-reactive groups comprised in the reaction mixture, but notthe isocyanate group itself.

The unfinished sandwich component is then placed into a mold, and thepolyurethane reaction mixture is hardened. The mold temperature here isless than 110° C. The mold temperature is preferably from 40 to 110° C.,with preference from 50 to 100° C., and particularly preferably from 65to 90° C.

The unfinished sandwich components are, if appropriate, laminated to anouter layer or to a decorative layer. The outer layer or the decorativelayer here can be applied to one side or to both sides of thepolyurethane sandwich component. As an alternative, the outer layer orthe decorative layer can be applied after the demolding of thepolyurethane sandwich component, in a further operation.

Examples of a decorative layer that can be used here are textiles havinga barrier to polyurethane saturation, compact or foamed plastics foils,and also polyurethane spray skins or polyurethane RIM skins. Outerlayers that can be used are preformed materials also suitable foroutdoor applications, e.g. metal foils or metal sheets, and also compactthermoplastic composites composed of PMMA (polymethyl methacrylate), ASA(acrylate-modified styrene-acrylonitrile terpolymer), PC(polycarbonate), PA (polyamide), PBT (polybutylene terephtalate), and/orPPO (polyphenylene oxide) in coated, coatable, or colored form. Otherouter layers that can be used are outer layers produced continuously orbatchwise and based on polyurethane resins, on melamine-phenol resins,on phenol-formaldehyde resins, on epoxy resins, or on unsaturatedpolyester resins.

Another great advantage of the inventive process is that by virtue ofthe reduced mold temperature it is also possible to use relativelyheat-sensitive decorative layers for lamination to the unfinishedsandwich components, examples being PVC (polyvinyl chloride), TPU(thermoplastic polyurethane), polyesters, and automobile-carpetmaterials, and there is no need to delay application of these to asubsequent step, using an adhesive.

The polyurethane sandwich components produced by a process of theinvention can by way of example be used as structural components orcladding components, in particular in the automobile industry, in thefurniture industry, or in the construction industry.

The unfinished sandwich components are, if appropriate, trimmed onlamination by way of what are known as flash faces or pinch edges, andno further downstream operations, such as stamping or milling, are thenneeded here.

In particular, when reactive chain extenders (e) are used, polyurethanesandwich components of the invention feature not only the advantage oflow processing temperature but also improved edges when compared withcomponents which have been produced without use of reactive chainextenders (e) of the invention. Furthermore, there is less penetrationof the polyurethane mixture into the core layer when reactive chainextenders (e) are used, the result here therefore being a saving ofmaterial and lower weight of the sandwich components.

The use of reactive chain extenders (e) also leads to reducedcontamination of plant during production of the polyurethane sandwichcomponents, since there is less tendency for material to drip from theunfinished sandwich components.

The examples are intended to illustrate the present invention.

-   Polyol 1: polyether polyol whose OH number is 555 mg KOH/g, prepared    via addition of PO onto glycerol.-   Polyol 2: polyether polyol whose OH number is 935 mg KOH/g, prepared    via addition of EO onto trimethylolpropane.-   Polyol 3: polyether polyol whose OH number is 400 mg KOH/g, prepared    via addition of EO/PO onto sucrose/diethylene glycol mixture.-   Stabilizer: Tegostab® B8443, silicone stabilizer, GE Bayer Silicones-   Catalyst 1: N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine-   Catalyst 2: adipic salt of    N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine in ethylene glycol-   Catalyst 3: diethyltoluenediamine-   Dye: Isopur® SU-12021/9111, ISL-Chemie-   Polyisocyanate: Lupranat® M20W, BASF SE

Catalyst 2 here was prepared as follows:

900 g of adipic acid were weighed into a 514-necked round-bottomed flaskand slurried in 2100 g of ethylene glycol. The entire system was heatedto 70° C. with stirring at reflux in an oil bath and then 1000 g ofN,N-bis(3-dimethylaminopropyl)-N-isopropanolamine were added slowly withthe aid of a dropping funnel. This caused further heating of themixture, and the adipic acid which had hitherto merely been slurriedunderwent reaction to dissolve in the ethylene glycol. A reddish viscousliquid formed.

Mixing specification 1: (of the invention) Polyol component Polyol 130.20 parts by weight Polyol 2 25.00 parts by weight Polyol 3 34.00parts by weight Stabilizer 0.40 parts by weight Water 0.40 parts byweight Catalyst 1 parts by weight Catalyst 2 4.00 parts by weightCatalyst 3 2.00 parts by weight Dye 4.00 parts by weight Isocyanatecomponent Polyisocyanat 200.00 parts by weight

The average OH number of the polyol mixture (polyols 1 to 3) is600^(mg KOH)/g

Mixing specification 2: (comparison) Polyol component Polyol 1 35.80parts by weight Polyol 2 25.00 parts by weight Polyol 3 34.00 parts byweight Stabilizer 0.40 parts by weight Water 0.40 parts by weightCatalyst 1 0.40 parts by weight Catalyst 2 Dye 4.00 parts by weightIsocyanate component Polyisocyanat 200.00 parts by weight

The average OH number of the polyol mixture (polyols 1 to 3) is598^(mg KOH)/g

EXAMPLE 1 Of the Invention

The polyol component and the isocyanate component according to mixingspecification 1 were mixed with one another by means of a high-pressurespray system, and spray-applied to a prepared semifinished sandwichproduct. Specifically, ˜225 g/m² of PU reaction mixture was sprayed ontoboth sides of an expandable honeycomb paperboard of thickness 17 mm,both sides of which had been covered with 225 g/m² of random glass mat.The unfinished sandwich component was then pressed in a mold heated to85° C. to a component thickness of 15.5 mm and demolded after 60 s. Thepolyurethane sandwich component obtained after demolding had very goodedges, particularly in sharp-edged regions.

COMPARATIVE EXAMPLE 1

Starting from mixing specification 2, the procedure was analogous tothat of example 1. Prior to insertion into the mold, a considerableportion of the spray-applied reaction mixture dripped from theunfinished sandwich component. The molding obtained on demolding after60 s appeared not to be fully hardened.

COMPARATIVE EXAMPLE 2

Starting from mixing specification 2, the procedure was analogous tothat of example 1, with pressing for 60 s at a mold temperature of 130°C. Here again, a considerable portion of the spray-applied reactionmixture dripped from the unfinished sandwich component. The componentobtained after demolding after 60 s was a fully hardened polyurethanesandwich component with distinct defects at the edges.

The invention claimed is:
 1. A polyurethane sandwich component obtainedby a process of (i) applying a polyurethane system to at least onereinforcement fiber layer on a core layer, to yield a first component,(ii) placing the first component from (i) into a mold, and giving thefirst component from (i) a three-dimensional shape by compressing thecore layer in the mold, and hardening the polyurethane system, to yielda molding, (iii) removing the molding from the mold, and (iv)optionally, subjecting the molding to further operations, wherein thepolyurethane sandwich component comprises the core layer and thepolyurethane system, the polyurethane system comprising: a) at least onepolyisocyanate; b) at least one isocyanate-reactive compound; c) atleast one carboxylic salt of an amine catalyst; d) optionally, at leastone further catalyst; e) optionally, a reactive chain extendercomprising at least two groups reactive toward isocyanates, wherein atleast one group reactive toward isocyanates is a free, primary NH₂group; and f) optionally, at least one further additive, and, based onone equivalent of amine of the amine catalyst, from 0.5 to 1.5equivalents of acid groups of a carboxylic acid are comprised.
 2. Thepolyurethane sandwich component according to claim 1, wherein thecarboxylic acid is a dicarboxylic acid of a formula HOOC—(CH₂)_(n)—COOH,where n is a whole number from 2 to
 14. 3. The polyurethane sandwichcomponent according to claim 2, wherein the amine catalyst c) has atleast one isocyanate-reactive group.
 4. The polyurethane sandwichcomponent according to claim 2, wherein the reactive chain extender e)is comprised in the polyurethane system at from 0.1 to 10% by weight,based on the total weight of components b) to f).
 5. The polyurethanesandwich component according to claim 2, wherein the carboxylic acid isadipic acid.
 6. The polyurethane sandwich component according to claim5, wherein the amine catalyst c) has at least one isocyanate-reactivegroup.
 7. The polyurethane sandwich component according to claim 5,wherein the reactive chain extender e) is comprised in the polyurethanesystem at from 0.1 to 10% by weight, based on the total weight ofcomponents b) to f).
 8. The polyurethane sandwich component according toclaim 1, wherein the amine catalyst c) has at least oneisocyanate-reactive group.
 9. The polyurethane sandwich componentaccording to claim 1, wherein the reactive chain extender e) iscomprised in the polyurethane system at from 0.1 to 10% by weight, basedon the total weight of components b) to f).
 10. The polyurethanesandwich component according to claim 1, wherein from 0.7 to 1.3equivalents of acid groups are present based on one equivalent of theamine of the amine catalyst.
 11. The polyurethane sandwich componentaccording to claim 1, wherein from 0.9 to 1.10 equivalents of acidgroups of the carboxylic acid are present based on one equivalent of theamine of the amine catalyst.
 12. The polyurethane sandwich componentaccording to claim 1, wherein, based on one equivalent of amine of theamine catalyst, from 0.5 to 0.95 equivalents of acid groups of acarboxylic acid are comprised.
 13. The process according to claim 12,wherein, based on one equivalent of amine of the amine catalyst, from0.5 to 0.95 equivalents of acid groups of a carboxylic acid arecomprised.
 14. The process according to claim 12, wherein, based on oneequivalent of amine of the amine catalyst, from 0.5 to 0.9 equivalentsof acid groups of a carboxylic acid are comprised.
 15. The polyurethanesandwich component according to claim 1, wherein, based on oneequivalent of amine of the amine catalyst, from 0.5 to 0.9 equivalentsof acid groups of a carboxylic acid are comprised.
 16. A process for theproduction of a polyurethane sandwich component, comprising: i) applyinga polyurethane reaction mixture to at least one reinforcement fiberlayer on a core layer, to yield a first component; ii) placing the firstcomponent from i) into a mold, and giving the first component from i) athree-dimensional shape by compressing the core layer in the mold, andhardening the polyurethane reaction mixture, to yield a molding; iii)removing the molding from the mold; and iv) optionally, subjecting themolding to further operations, wherein the polyurethane reaction mixtureis obtained via mixing of the components of the polyurethane systemcomprising: a) at least one polyisocyanate; b) at least oneisocyanate-reactive compound; c) at least one carboxylic salt of anamine catalyst; d) optionally, at least one further catalyst; e)optionally, a reactive chain extender comprising at least two groupsreactive toward isocyanates, wherein at least one group reactive towardisocyanates is a free, primary NH₂ group; and f) optionally, at leastone further additive, and wherein, based on one equivalent of amine ofthe amine catalyst, from 0.5 to 1.5 equivalents of acid groups of acarboxylic acid are comprised.
 17. The process according to claim 16,wherein mold temperature is below 110° C.
 18. The process according toclaim 17, wherein the carboxylic acid is a dicarboxylic acid of aformula HOOC—(CH₂)_(n)—COOH, where n is an integer from 2 to
 14. 19. Theprocess according to claim 17, wherein the carboxylic acid is adipicacid.
 20. The process according to claim 17, wherein the mold in ii)comprises a decorative element.
 21. The process according to claim 16,wherein the mold in ii) comprises a decorative element.
 22. The processaccording to claim 21, wherein the carboxylic acid is a dicarboxylicacid of a formula HOOC—(CH₂)_(n)—COOH, where n is an integer from 2 to14.
 23. The process according to claim 16, wherein the carboxylic acidis a dicarboxylic acid of a formula HOOC—(CH₂)_(n)—COOH, where n is aninteger from 2 to
 14. 24. The process according to claim 16, wherein thecarboxylic acid is adipic acid.
 25. The process according to claim 16,wherein the amine catalyst c) has at least one isocyanate-reactivegroup.
 26. The process according to claim 16, wherein the reactive chainextender e) is comprised in the polyurethane system at from 0.1 to 10%by weight, based on the total weight of components b) to f).
 27. Theprocess according to claim 16, wherein from 0.7 to 1.3 equivalents ofacid groups are present based on one equivalent of the amine of theamine catalyst.
 28. The process according to claim 16, wherein from 0.9to 1.10 equivalents of acid groups of the carboxylic acid are presentbased on one equivalent of the amine of the amine catalyst.